Have you ever wondered. . . is there a player in RuneScape so rich, so mind-bendingly wealthy that he is effectively the living embodiment of the RuneScape economy? Is such a thing even possible? No, it couldn't be. Only a Jagex employee could even have any sort of remote chance of coming anywhere near as close to how rich I'm talking about. But what if somewhere, deep within the 200m accounts created in RuneScape, there was a player who defied all odds and effectively did what everyone thinks is impossible and became the single richest person in ALL of RuneScape. Jagex themselves might have to bow their heads down to his might, for if he chooses to do so, he could send RuneScape into an even bigger economic crisis than what's currently going on. Banning him and freezing his account won't do any good, because all the damage control would be FAR too costly for them to even attempt.

But how rich am I talking? I'm talking:

Max partyhat stacks
Max christmas cracker stack
Max spirit shard stack
Max spirit shard pack stack
Max stacks of every single rare item in the entire game
Max stacks of every single high-value commodity in the game (god wars items, drygore weaponry, dragon items, the list goes on)
Max stacks of virtually everything of moderate value and high demand, right down to simple things like needles, buckets, and tinderboxes, because gp is acquired so quickly that it has to be re-allocated into something that can retain its GP value.

This person has acquired a position SO high up on the wealth scale, that a max cash stack will without a doubt look like 1gp from his standpoint, because it can be so easily obtainable. He could give away 10 max cash stacks a day, but could come back with 15 at the end of the day. THAT'S how wealthy of a player I'm talking about.

Doubt it, because the only way to get max party hat stacks would be to start collecting before they were too pricey. And back then I don't think anybody really went for 'max' anything. (Max as in 2.14B)

It is possible to merchant more money everyday but eventually you are limited. There is a 1 or 2 per 4Hr buy limit on party hats, which can be flipped for under 20M each. And you are limited to 6 G.E. slots. (Assuming this person doesn't transfer wealth between accounts.)
I assume max drygore doesn't exist yet .

And if such a player did exist they would have already been rolled back by Jagex, because he is too influential. Or succumbed to selling his gold, because let's face it just 'Max Shards' is currently valued over 10 thousand USD (Assuming 20-25c/M), if my math is correct.
To elaborate on that, if people didn't know such an account existed it would have no effect on the short-term economy, and this being a game the long-term economy is always up in the air.

Of course not. Given that there are 86400 seconds in a day, and the early rare drop events lasted only a day, there would need to be 24855 rares dropped per second on the day of the eventfor there even to be a single max stack of that item to exist, let alone multiple.

I don't see how it would be possible for anyone to accumulate that much wealth using legit methods; maybe a player could get very rich doing things like luring, scamming, bug abusing or hosting flowers but I still don't think they could reach the level of wealth you are talking about. They would also run the risk of Jagex taking action against them, removing the wealth and redistributing the items/rares through the ge and that would remove their influence over the economy.

Some players do have huge collections of everyday items, like tinderboxes that you mentioned, and this influences the item's ge price. For instance the guy in this thread has a large collection of pestle and mortar and his buying them has contributed to their price rising dramatically. In the past there were also merch clans which could have a short-term influence on prices. People who collect items can have such an impact as they manage to to gain control of a large amount of the total items available. I do not think a single player could accumulate enough gp to have an influence over the Runescape economy like this, the amount of gp in the game is simply too large for even the very richest of players to have a sizable proportion of it.